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Relevant academic research and scientific papers

Electron-Transfer Quenching of the Luminescent State of the Tris(bipyridyl)ruthenium(II) Complex in Micellar Media

Observations of the orange luminescence from the excited state of Ru(bpy)3(2+) ions have been used to follow the photoredox reaction between this species and methyl (and other N-alkyl) viologen ions dispersed in aqueous and micellar media.Time-resolved experiments show that the luminescence decays in an exponential manner both in water and in micellar media composed of the surfactant sodium dodecyl sulfate even under conditions where the quencher distribution about micelles should require nonexponential behavior.The rate constants in H2O clearly showed a kinetic salt effect.The effect of viologen concentration could be interpreted in terms of the quenching process occurring within the diffuse double layer of the micelles.This was supported by observations of the decay of the photoredox products using kinetic absorption spectrophotometry.In reverse micelles formed from Aerosol OT in heptane or cyclohexane, exponential decay of the luminescence was only observed at low methyl viologen concentrations.At concentrations above ca. 2 mM (varied with water content) double exponential behavior was observed.With duroquinone as quencher in the reverse micellar system, quenching occurred but no indication of the ionic products of the photoredox process was found.This indicates that duroquinone partitions into the aqueous pool of the reverse micelles and no phase transfer of electrons or product ions is occurring.

Salt and solvent effects on the kinetics of the oxidation of the excited state of the [Ru(bpy)3]2+ complex by S2O 82-

The title reaction was studied in different reaction media: aqueous salt solutions (NaNO3) and water-cosolvent (methanol) mixtures. The observed rate constants, kobs, show normal behavior in the solutions containing the electrolyte, that is, a negative salt effect. However, the solvent effect is abnormal, because a decrease of the rate constant is observed when the dielectric constant of the reaction medium decreases. These effects (the normal and the abnormal) can be explained using the Marcus-Hush treatment for electron transfer reactions. To apply this treatment, the true, unimolecular, electron-transfer rate constants, ket, have been obtained from kobs after calculation of the rate constants corresponding to the formation of the encounter complex from the separate reactants, kD, and the dissociation of this complex, k-D. This calculation has been carried out using an exponential mean spherical approach (EMSA).